Method of making a limited-rotation motor with integral displacement transducer

Abstract

The armature of a limited-rotation motor which rotates about an axis relative to a stator is extended axially beyond the stator between arcuate, non-magnetic capacitor plates disposed in a cylindrical array coaxial with the rotation axis. The capacitor plates are connected in a bridge circuit whose output is a selected function of armature displacement. The capacitor plates are installed at the end of the motor stator during assembly of the motor as tines of a unitary slotted bushing that is reamed simultaneously with the motor stator, following which the bushing is circumferentially cut to electrically isolate the bushing tines to form the individual plates.

I claim: 
     
       1. The method of making a limited rotation motor of the type having a stator with stator pole pieces forming a generally cylindrical passage extending axially along the stator and an armature rotatively mounted in the passage and biased toward a reference position, said method comprising the steps of A. forming an elongated bushing out of electrically conductive nonferromagnetic material, said bushing having a generally cylindrical inner surface whose radius is substantially the same as that of said passage,   B. forming lengthwise slots in the bushing so as to define at least one pair of arcuate tines extending from the bushing collar,   C. assembling the stator pole pieces and bushing so that the bushing is coaxial with the axis of said passage,   D. potting the pole pieces and bushing in a nonelectrically conductive material so as to maintain their spatial relationship and to define a single cylindrical passage extending through the bushing and pole pieces,   E. forming a circular cut in the bushing so as to separate the bushing tines from the bushing collar and from each other so as to electrically isolate them, and   F. honing the entire passage so that the separated bushing tines and pole pieces have the same radius all along said passage and are concentric with the passage axis over their entire areas so that when the armature is rotated, the differential capacitance between the plates and the armature accurately reflects the angular deviation of the armature from its reference position.   
     
     
       2. The method defined in claim 1 A. wherein the bushing is slotted to form two pairs of diametrically opposite coextensive tines, and   B. including the additional step of electrically connecting said opposite tines together prior to the potting step.   
     
     
       3. The method defined in claim 1 and including the additional step of forming the motor armature so that it is coextensive with the passage defined by the pole pieces and bushing tines. 
     
     
       4. The method defined in claim 3 and including the additional steps of A. providing an electrically conductive spring anchored between the bushing and the armature to bias the armature to its reference position,   B. connecting an electrical lead to the member to effect an electrical connection to the armature by way of said spring, and   C. connecting additional, separate, electrical leads to the bushing tines prior to the potting step.   
     
     
       5. The method defined in claim 4 and further including rotatively supporting said armature end in said bushing collar beyond the bushing tines.